Cellular nitrocellulose based composition and method of making

ABSTRACT

NOVEL, SMOKELESS, COMBUSTIBLE, CONSUMABLE COMPOSITIONS ARE PRODUCED BY MIXING A NITROCELLULOSE BASED EXPLOSIVE WITH AN ORGANIC POLYISOCYANATE IN THE PRESENCE OF A LIQUID PLASTICIZER AT AN ELEVATED TEMPERATURE.

United States Patent ()fiice' 3,711,343 Patented Jan. 16, 1973 ABSTRACT OF THE DISCLOSURE Novel, smokeless, combustible, consumable compositions are produced by mixing a nitrocellulose based explosive with an organic polyisocyanate in the presence of a liquid plasticizer at an elevated temperature.

l The invention described herein may be manufactured, used and licensed by or for the Government for governmental purposes without the payment to us of any royalties thereon. l

DESCRIPTION OF THE INVENTION The present invention relates to a totally consumable, smokeless, combustible composition and to the methods of making the same. More particularly the invention is concerned with combustible material that may be formed in the shape of and serve as combustible cartridge cases or the like.

The advantages of combustible cartridge cases will. be apparent to those skilled in the art. The firing ratesof weapons in which combustible cartridge cases are used may be increased substantially due to the elimination of the ejection operation which would also result in a saving of weight and space in the weapon. The problem of disposal of metal shell cases is eliminated, creating thereby a saving of metals which might become critically short in supply during times of emergency. Furthermore, the elimination of the conventional metal case results in a cdnsiderable saving in weight. An additional advantage of combustible cartridge cases may involve the possible reduction in gun erosion. Yet another use of combustible casing material would be in the manufacture of rocket casing that would be consumed as the rocket fuel was burned, thus eliminating a considerable dead weight found in prior metal rocket casings.

Although use as a casing material is a principal object, other possible uses include the production of primer tubes and obturators, the potting of strands for tensile testing, the case bonding of nitrocellulose based propellants and the production of a thin sheet to be used as a substitute for cloth powder bags.

Prior combustible casings were found to be unsatisfactory because of one or more of the following deficiencies: excessive residue, incomplete burnout, failure to produce an effective vapor barrier and/or the production of smoke.

Previous methods of manufacture of consumable compositions required separate mixing of selected resins, explosives and blowing agents and then a subsequent combination of these items. This type of process was time consuming, expensive and required extensive solvent removal.

Accordingly, a primary object of the present invention is the provision of a combustible composition, which when used as a cartridge casing will burn completely when fired in conventional weapons.

Another object of this invention is to provide a combustible composition which has superior strength while maintaining a good burning rate.

Yet another object of this invention is to provide a combustible composition which will not generate smoke.

A still further object of this invention is to provide a process for the production of a consumable composition which is simple, eflicient and inexpensive.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same become better understood by reference to the following detailed description.

According to the present invention, novel combustible compositions are obtained by mixing a small amount of an organic polyisocyanate with a nitrocellulose base propellant in the presence of an organic liquid plasticizer and preferably also, an opacifying agent, and heating the resultant viscuous liquid mixture before or after it is poured into molds to cure. During the mixing and/or curing operations, the organic polyisocyanate reacts with the moisture normally present in the nitrocellulose and which may be present in other ingredients e.g. (liquid plasticizer or opacifying agent), thereby generating gaseous carbon dioxide which is more or less uniformly distributed throughout the mass imparting a cellular structure thereto. Further the excess polyisocyanate not consumed in the above reaction, reacts with the hydroxyl group of the nitrocellulose polymer to crosslink such polymers and thereby increase the strength and dimensional stability of the foamed nitrocellulose.

The foamed nitrocellulose thus obtained is completely combustible, smokeless, essentially residue free and is particularly suited for the manufacture of non-metallic cartridge cases.

Nitrocellulose base propellants which have been found to be effective include single base ball powder [98.0% nitrocellulose (12.6% nitrogen content), 1.0% diethylphthalate, 1.0% 2-nitrodiphenylamine, and 0.1% dioctylphthalate (added)] and double base ball powder [89.76% nitrocellulose, 8.59% nitroglycerine, 1.65% Z-nitrodiphenylamine, and 0.53% carbon black (added)].

The plasticizer can be an oxidant-type liquid containing active oxidizing groups such as nitro, nitrate, nitrite and nitroso groups, e.g. nitroglycerine diethylene glycol dinitrate, pentaerythritol trinitrate, 1,2,4-trinitro-butane and the like, or inert organic liquid plasticizers, which function as an additional fuel component, as, for example, sebacates, such as dibutyl sebacate and dioctyl sebacate; phthalates, such as dibutyl phthalate and dioctyl phthalate; adipates, such as dioctyl adipate and dinormal propyl adipate; glycol esters of fatty acids and combinations of the above such as casting solvent x (34.0% 1,2,3-butane-triol trinitrate, 65.0% triethylene glycol dinitrate and 1.0% 2-nitrodiphenylamine) Substantially any reactive organic polyisocyanate can be employed, including aliphatic diisocyanates, such as hexamethylene diisocyanate, and aromatic polyisocyanates, such as 2,4-tolylene diisocyanate, mixtures of 2,4- tolylene diisocyanate and 2,6-tolylene diisocyanate, mphenylene diisocyanate, 3,3 bitolylene-4,4'-diisocyanate, diphenylmethane 4,4'-diisocyanate, dianisidine diisocyanate, and 1,5-naphthalene diisocyanate.

The particular polyisocyanate selected is generally determined to a considerable extent by its reaction rate in a given reaction system and the properties which it imparts to the final polymer product. In a highly reactive system, the use of a somewhat less reactive aliphatic diioscyanate, such as hexamethylene diisocyanate can be advantageous to prevent excessive exotherm or to prevent excessive hardening of the polymeric structure before good cell formation is obtained. In general, the aromatic diisocyanates are preferred because of their more rapid reaction rates, and, in particular, 2,4- or a mixture of 2,4- and 2,6-tolylene diisocyanate, because of its excellent performance, availability and low cost.

The amount of polyisocyanate employed for the combustlble composition will vary as it is a function of the amount of water found in the other ingredients and the structural rigidity and dimensional stability desired. Sufficient polyisocyanate must be provided to react with not only all the Water present but also to react with the hydroxyl g ps of the nitrocellulose base propellant to eifect cross linking of the nitrocellulose polymer and produce a Solid cellular composition of increased strength and rigidity.

Additives such as PETN (pentaerythrite tetranitrate), RiDX (cyclotrimethylenetrinitramine), or HMX (cyclott'etramethylenetetranitramine) may be used to increase "burning rates.

Carbon black or other pigments known to the art may be added to provide opacity to the combustible composiion.

Although it is not intended that the invention be limited thereto, there is set forth herein below for purposes of illustration, examples of various consumable compositions and. methods for production thereof.

EXAMPLE I Compounds: In composition, percent Single base ball powder* 70.2 Dinormal propyladipate 27.8 2,4-tolylene dissocyanate 2.0 Carbon black (added) 0.02

38.0% nitrocellulose (12.6% nitrogen content) 1.0% diethylphthalate, 1.07 2-nitr0di hen lamine, and 0.1 dio tylphtliaiate (addedf. p y c Procedure The single base ball powder, dinormal propyladipate and carbon black are mixed together in a vertical sigma blade mixer at ambient temperature for about /2-1 hour until a homogeneous slurry is achieved. To the slurry is added the tolylene diisocyanate and the ingredients are again mixed for about V2 hour to ensure a homogeneous mixture. Thereafter the composition is mixed at an elevated temperature, approximately 90 F., until a casti- --ble viscosity is achieved (approximately 30,000 centipoise). The mixture is then cast into molds of preferred 'I 'he same as Example I except the diethylene glycol dinitrate is substituted for the dinormal propyladipate.

EXAMPLE III Compounds: In composition, percent Double base ball powder* 60.0 Triethylene glycol dinitrate 19.0 Nitroglycerine 19.0 2,4-tolylene diisocyanate 2.0 Carbon black (added) 0.02

*9.76% nitrocellulose, 8.59% nitroglycerine, 1.65% 2-nitrodiphenyl amlne and 0.53% carbon black (added).

Procedure The double base ball powder, triethylene glycol dinitrate, nitroglycerine and carbon black are mixed together at ambient temperature in a vertical sigma blade mixer for approximately one hour. The 2,4-tolylene diisocyanate is then added to the composition and mixed for /2 hour to ensure homogeneity. The temperature is elevated to about F. and the mixing continued'until a casting viscosity is achieved. The composition is poured into a selected mold and the samples then cured for 24 hours at 72 C.

"As in Example III.

Procedure The same as Example III with the substitution of trimethylolethane trinitrate instead of nitroglycerine.

EXAMPLE V Compounds: 7 In composition, percent Double base ball powder 1 60.0 l Casting solvent x 2 38.0 1 2,4-tolylene diisocyanate 2.0 j Carbon black (added) 0.2

JAs in Example III. 3 34.0% 1,2,4-butanetriol trlnitrate, =65.0% triethylene glycol dinitrate and 1.0% 2 nitro-diphenylamine.

Procedure I As in Example I with the substitution of solvent x instead of the'dinormal propyladipate. EXAMPLE v1 Compounds: In composition, percent 1 Double base ball powder* 68.0 t Casting solvent x* 30.0 2,4-tolylene diisocyanate 2.0 Carbon black (added) 0.2 l "As in Example V. Procedure l As in Example I with the substitution of solvent x instead of the dinormal propyladipate.

1 Although, in the above examples, foaming was accomlished at the mixing stage, it may also take place at the curing stage. This is accomplished by mixing the nitrocellulose base ball powder, liquid plasticizer and polyisocyariate at ambient temperature and pouring the homogeneous mixture into heated molds (approximately 72 C.) under 4000 p.s.i. At this elevated temperature foaming will occur while the composition is curing.

Further, although the preferred temperature to attain a casting viscosity is about 90 E, a temperature between 7590 F. may be used without any appreciable variation in foaming action. Above 90 F., curing will take place which is detrimental to any mixing.

The percent composition of the ingredients may be varied somewhat without any variation in performance. The nitrocellulose base ball powder may be varied from 50-75% with optimum results occurring in the 6070% range. The organic polyisocyanate because of variations in moisture content of the ingredients and because of the structural rigidity required, may be varied from 14%. Optimum results as to foaming and strength occur at about 2%. And finally the plasticizer may be varied from 5-50% with optimum results occurring between 27-38%.

Thusly through the practice of our invention a composition is produced which is combustible, essentially consumable (almost totally consumed when single base ball powder is used, totally consumed when double base ball powder is used), does not generate smoke and has the added advantage of strength due to the cross linking of nitrocellulose bonds.

From the above examples and disclosure it is apparent that compositions made in accordance with this invention are capable of being formed or shaped into tubes, solid cylinders or other shapes by the use of appropriate molds. The product resulting thereby is a combustible material suitable for use for such items as combustible cartridge cases, combustible primers, combustible initiators and other items where the combustion of the item in use is desirable or required.

We wish it to be understood that we do not desire to be limited to the exact details and compositions described in this specification for obvious modification will occur to a person skilled in the art.

We claim:

1. A process for producing a solid, crosslinked, cellular nitrocellulose base propellant composition which comprises:

Mixing an organic polyisocyanate selected from the group consisting of hexamethylene diisocyanate, 2,4- tolylene diisocyanate, mixtures of 2,4-tolylene diisocyanate and 2,6-tolylene diisocyanate, m-phenylene diisocyanate, 3,3 bitolylene 4,4-diisocyanate, diphenylmethane 4,4 diisocyanate, dianisidine diisocyanate and 1,5-naphthalene diisocyanate with a finely divided nitrocellulose base propellant selected from the group consisting of single base ball powder and double base ball powder and an inert liquid organic plasticizer for said propellant to produce a slurry, the amount of said polyisocyanate being sufiicient to react with (l) the water normally present in said propellant and said plasticizer and (2) hydroxyl groups of the nitrocellulose propellant;

heating said slurry to react the polyisocyanate with (1) said water to generate carbon dioxide and produce a foamed viscous product and (2) hydroxyl groups of the nitrocellulose propellant to crosslink said nitrocellulose polymer, and curing the resultant product to produce a solid, crosslinked, cellular, nitrocellulose base propellant composition.

2. The process of claim 1 wherein the mixing and heating of the slurry are eflected simultaneously.

3. The process of claim 1 wherein the heating of the slurry takes place at the curing stage.

4. The process of claim 1 wherein the nitrocellulose base propellant and the plasticizer are pre-mixed prior to mixing with the organic polyisocyanate.

5. The process of claim 1 wherein the nitrocellulose base propellant, plasticizer and orgenic polyisocyanate are mixed simultaneously.

6. The process of claim 1 wherein the slurry is heated to a temperature of between 75-90" F. during mixing.

7. The process of claim 1 wherein the slurry is cured at about 72 C. for approximately 18 hours.

8. The process of claim 1 wherein the plasticizer is selected from the group consisting of phthalates, seba-' cates, adipates, glycol esters of higher fatty acids and oxidant-type liquids containing nitro, nitrate, nitrite and nitroso groups.

9. The process of claim 1 wherein carbon black is added to the slurry.

10. A solid cellular nitrocellulose base propellant composition suitable as a combustible cartridge case consisting essentially of the cross-linked reaction product of an organic polyisocyanate, selected from the group consisting of hexamethylene diisocyanate, 2,4-tolylene diisocyanate, mixtures of 2,4-tolylene diisocyanate and 2,6-tolylene diisocyanate, m-phenylene diisocyante, 3,3-bitolylene-4,4-diisocyanate, diphenylmethane-4,4'-diisocyanate, dianisidine diisocyanate and 1,5-naphthalene diisocyanate, a nitrocellulose base propellant selected from the group consisting of single base ball powder and double base ball powder and an inert liquid organic plasticizer wherein said ingredients are present in the following percentages by weight: nitrocellulose base propellant 50%-75% organic polyisocyanate l%-4% and liquid organic plasticizer 5%50%.

11. The composition of claim 10 wherein the plasticizer is selected from the group consisting of sebacates, phthalates, adipates, glycol esters of higher fatty acids and oxidant-type liquids containing nitro, nitrate, nitrite and nitroso groups.

12. The composition of claim 10 wherein the organic polyisocyanate is selected from the group consisting of hexamethylene diisocyanate, 2,4-tolylene diisocyanate, mixtures of 2,4-tolylene diisocyanate and 2,-6-tolylene di isocyanate, m-phenylene diisocyanate, 3,3'-bitolylene-4,4'-

diisocyanate, diphenylmethane-4, 4'-diisocyanate, dianisidine diisocyanate and LS-naphthalene diisocyanate.

. 13. The process of claim 1 wherein the organic polyisocyanate is 2,4-tolylene diisocyanate.

14. The composition of claim 11) wherein the organic polyisocyanate is 2,4-tolylene diisocyanate.

15. A process for producing a solid cross linked, cellular nitrocellulose base propellant composition which comprises:

mixing between l%4% by weight of an organic poly- 3O isocyanate selected from the group consisting of hexarnethylene diisocyanate, 2,4-tolylene diisocyanate, mixtures of 2,4-tolylene diisocyanate and 2,6-

tolylene diisocyanate, mphenylene diisocyanate,

3,3-bitolylene 4,4 diisocyanate, diphenylmethane- 351 4,4-diisocyanate, dianisidine diisocyanate and 1,5-

. naphthalene diisocyanate 50%-75% by weight of a nitrocellulose base propellant selected from the group consisting of single base ball powder and double 1 base ball powder, and 5%5*0% by Weight of an inert liquid organic plasticizer to produce a slurry,

' the amount of said polyisocyanate being sufiicient to react with (l) the water normally present in said propellant and said plasticizer and (2) hydroxyl groups of the nitrocellulose propellant;

heating said slurry to react the polyisocyanate with 1) said water to generate carbon dioxide and produce a foamed viscous product and (2) hydroxyl groups of the nitrocellulose propellant to crosslink said nitrocellulose polymer, and

curing the resultant product to produce a solid, crosslinked, cellular, nitrocellulose base propellant composition.

References Cited UNITED STATES PATENTS 3,361,689 l/l968 Miegel et al. l49-l9 3,445 ,3 06 5/ 1969 Satriana 149-96 3,554,820 1/1971 Evans 149l9 X CARL D. QUARFORTH, Primary Examiner S. J. LECHERT, JR., Assistant Examiner US. Cl. X.R. 

